1. Field of the Invention
This invention relates to a system for discriminating the front surface of a tape from the back surface thereof, and more particularly to a system for discriminating between the front and back surfaces of a tape over the entire length thereof in a reliable and easy manner. The term "tape" as used herein means a flexible strip recording medium in the form coiled or wound around a core or delivered from a coiled roll, and broadly embraces magnetic tapes, continuous photographic films and the like.
2. Description of the Prior Art
In general, when preparing a tape as described above, a length 2 to 50 times that of the final product is coiled or wound around a ring-shaped core (hereinafter referred to as the continuous tape hub). Then, a specified length portion of the wound continuous tape is rewound around another ring-shaped core (hereinafter referred to as the product tape hub) suitable for the intended application, and sold in this form. The flexible strip recording medium described above is generally in the form of a tape having a width of about 3 to 51 mm, a length of about 45 to 3,000 m and a thickness of about 3 to 50 .mu.m. Such a recording medium consists of a magnetic or photosensitive film or the like layered on a flexible substrate, and is used for recording and reproducing information. The flexible substrate is, for example, made of a plastic film of, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide, and polyamide; paper; paper coated or laminated with paper or an .alpha.-polyolefin having from 2 to 10 carbon atoms such as polyethylene, polypropylene or an ethylene-butene copolymer; or a metal foil such as aluminium, copper or tin foil or the like. Typically, such recording media include audio tapes, video tapes, data tapes, 8 mm cine-films and the like.
In general, as shown in FIG. 1, when rewinding the tape from the continuous tape hub to the product tape hub, a continuous tape hub 2 around which a tape 1 has been wound is fitted to an unwind shaft 3. The end of the tape 1 is passed over guide rollers 4, 6, and a length detecting roller 5, and fixed on a product tape hub 8 which engages with a wind-up shaft 7. Motors (not shown) coupled with the unwind shaft 3 and the wind-up shaft 7 respectively are then rotated to move and wind the tape 1 around the product tape hub 8. When the standard length portion of the tape has been wound around the product tape hub 8, the length detecting roller 5 issues a standard length signal to stop the unwind shaft 3 and the wind-up shaft 7. Thereafter, the tape 1 is cut in the standard length by a tape cutter 9 to separate the standard length of tape wound around the product tape hub 8. For this purpose, an apparatus called a winder is generally used.
However, the conventional apparatus of the type described above is disadvantageous as described below. The tape handled is as thin as 3 to 50 .mu.m, and flexible. In addition, the tape width is as small as 3 to 51 mm. Consequently, when the tape moves from the continuous tape hub 2 to the product tape hub 8, it is sometimes twisted turned upside down due to a change in the tape tension or waving movement. If this happens, the tape is wound around the product tape hub 8 in the upside-down condition with the front surface thereof facing back.
If an audio tape is wound around the product tape hub 8 with the front surface thereof facing back and used for recording, the recording head 10 will come into contact with the base layer 11 of the audio tape instead of the magnetic layer 12 thereof, as shown in FIG. 2. Thus, the sound information cannot be recoded on the magnetic layer 12. If a video tape is wound in the inappropriate condition as described above, an image cannot be recorded thereon for the same reason. In addition, it is difficult for the users to recognize during recording whether the sound or image information is actually being recorded. The users become aware of a problem only when reproducing the recorded information, at which time it may be too late for remedial action.
In the past, many methods have been proposed for eliminating the problem described above. For example, for audio tapes or the like, the front and back surfaces of the tape are visually checked at the leading and tail ends thereof when the tape is rewound from the continuous tape hub 2 to the product tape hub 8. Or, as shown in FIG. 3, a recording head 13, a reproducing head 14 and an erasing head 15 are arranged in contact with the tape between the guide roller 4 and the length detecting roller 5 so as to detect the electric input and output signals between the heads and the tape. Alternatively, as shown in FIGS. 4A and 4B, light from a light projector (not shown) is passed through an optical fiber 16 onto a tape surface in contact therewith. In the case of FIG. 4A, light from the light projector further passes through another optical fiber 17 to a light receiver (not shown). In the case of FIG. 4B, light passing through the optical fiber 16 cannot reach the light receiver. Thus the front and back surfaces of the tape are detected on the basis of the light signal between the light projector and the light receiver. Further, it has also been proposed to apply a voltage between two electrodes 18, 19 in contact with the tape and to detect the difference in electrical resistance between the two electrodes, as shown in FIGS. 5A and 5B. However, all of the conventional methods as described above are disadvantageous in that they can only detect the front and back surfaces of the tape at specific sections thereof. These conventional methods cannot reliably detect the front and back surfaces of the tape over the entire length thereof.
More specifically, with the visual check method as described above, it is not possible to recognize the front and back surfaces of the tape when the tape is rewound at a high speed. The method using the recording, reproducing and erasing heads tends to scratch the tape surface due to the friction between the tape and the heads. This conventional method is also disadvantageous in that, when the tape is rewound at a high speed, the electric input and output signals between the heads and the tape become unstable or the tape separates from the heads, causing erroneous judgment regarding the tape surfaces. The conventional optical fiber method described above is disadvantageous in that the moving tape is scratched due to the friction with the optical fibers and, in addition, the tape front and back surfaces cannot be detected correctly if the moving tape separates from the optical fibers. The conventional method based on the electrical resistance described above is also disadvantageous in that the tape suffers from scratches due to the friction with the electrodes and, moreover, the contact force between the electrodes and the tape becomes uneven when the tape moves. This uneven contact force causes erroneous judgment regarding the tape front and back surfaces.
To avoid the problems of the conventional methods described above, the front and back surfaces of the tape are generally investigated at the leading end and/or tail end of the tape only when the tape is stationary. This is done visually or by the optical fiber or electrical resistance method.
However, the conventional methods as described above cannot detect the front and back surfaces of the wound product tape at the central section thereof. With such conventional methods, it sometimes happens that the tape is inappropriately wound around the product tape hub with the front surface thereof facing back if the tape once gets twisted and then returns to the original position when moving from the unwind shaft 3 to the wind-up shaft 7. Such a faulty tape winding also occurs if the continuous tape sent from the previous process has already been turned upside down with the front surface thereof facing down. Further, for thin tapes such as audio and video tapes, it is impossible to discern an upside-down section of the tape even by visually examining the end faces of the wound-up tape with great care.